The invention relates to a resistor-capacitor-transistor type of integrated circuit. It can be applied notably to oscillators.
RC type circuits are used notably in relaxation oscillators. These oscillators have a capacitor that is charged by means of a resistor and discharged by means of a transistor. The sizes and values of these three discrete elements have a direct influence on the time taken to charge and discharge the capacitor. In particular, the greater the capacitance value of the capacitor, the slower the discharging operation and greater the size needed for the discharging transistor if the discharging is to take place as swiftly as possible. In practice, the discharging is highly dependent on the characteristics of the discrete elements (the capacitor and the transistor). With present-day technologies, the discharging thus requires a minimum of two to five nanoseconds for very large capacitance values of the order of 10 pF (10.times.10.sup.-12 farads). Now the charging and discharging time has a direct influence on the frequency that can be obtained with the relaxation oscillator. The frequency, therefore, is itself also dependent on the characteristics of the discrete charging and discharging elements and the minimum time taken to discharge the capacitor limits the frequency. Thus, with present-day technologies, a maximum of 10 to 20 megahertz are obtained at output of a relaxation oscillator.
Higher oscillation frequencies are however sought in certain applications, notably for microprocessors.
An object of the invention is a resistor-capacitor-transistor integrated circuit that enables discharging that is speedier and independent of the values of the resistance and capacitance values of the resistor and capacitor. For a given technology, there is a discharging time that is small and fixed, notably whatever the capacitance value of the capacitor.
The structure of the invention furthermore advantageously compact.